1. Field of Invention
This invention relates to the field of radio telephones typically cordless telephones and, more particularly, to an apparatus and method for enabling sounds to be heard from another telephone apparatus by means of a loudspeaker.
2. Description of the Prior Art
As is well known in the art, radio telephones, typically cordless telephones are comprised of a radio telephone set having a handset and a base unit connected to a wired telephone line for exchanging speech signals between the wired telephone line and the radio telephone set through a radio channel. The base unit and the radio telephone set are each provided with a pair of corresponding transmitters and receivers.
When a call signal arrives at the wired telephone line, the base unit transmits a paging signal to the radio telephone set through a predetermined control channel to form a speech channel. The paging signal includes a channel signal indicating one of a plurality of speech channels. Then, the radio telephone set starts an operation to send out a paging response signal through the control channel in response to the received paging signal. The base unit detects the intensity of the received paging response signal sent out from the radio telephone set, i.e., the intensity of the paging response signal at the control channel. Then, the base unit stops the transmission of the paging signal when the detected intensity exceeds a predetermined level and switches the radio channel between the base unit and the radio telephone set from the control channel to the speech channel indicated in the paging signal. The radio telephone set also switches the radio channel from the control channel to the speech channel by the received paging signal. Thereafter, the base unit transmits a ringing signal to the radio telephone set via the speech channel. After transmitting the ringing signal, the base unit establishes a speech path between the wired telephone line and the radio telephone set when it receives an "off-hook" signal from the radio telephone set indicating that the handset is "off the hook".
When the base unit is in a waiting state and receives a call origination signal (an off-hook signal) from the radio telephone set through the control channel, it determines the call origination request from the radio telephone set and transmits a response signal which includes the channel signal indicating one of the plurality of speech channels. Then, the base unit establishes a speech path between the wired telephone line and itself, and switches the radio channel from the control channel to the speech channel indicated in the response signal. After receiving the response signal, the radio telephone set also switches the radio channel from the control channel to the speech channel in response to the received response signal.
If, in this state, the radio telephone set transmits dialing signals to the base unit through the speech channel by a dialing operation, the dialing signal is transmitted to the wired telephone line via the base unit.
Thus, the radio telephone apparatus carries out the operations of receiving incoming telephone calls from the wired telephone line and originating calls from the radio telephone set.
However, the prior art radio telephones suffer a serious drawback in that a sufficiently large enough loudspeaker can not be adapted to be used in the apparatus because it is necessary for the radio telephone set to be compact and light. Even if a loudspeaker with a large enough speaker was adapted to be used in the apparatus, it is extremely difficult to drive the loudspeaker to generate speech signals because the capacity of the power source of the radio telephone set is not sufficient to drive the loudspeaker. Generally, the power source is a small storage battery used to drive the components of the radio telephone set. These components typically have low power requirements. Loudspeakers typically have high power requirements.